Production and accumulation of beta-hydroxy fatty acids and alpha, beta-unsaturated fatty acids during fatty acid beta-oxidation by aerobic and ischemic isolated perfused rabbit hearts and by isolated rabbit heart mitochondria will be measured. Gas liquid chromatography-mass spectrometry will be used to identify and measure these fatty acids. Production of these beta-oxidation intermediates will be correlated with beta-oxidation flux and the degree of heart ischemia. The intracellular distribution of these intermediates will be determined.